While synthetic detergents have widespread use in powdered and liquid form, until recently the use thereof has achieved only limited commercial success in displacing the familiar bars of household toilet or bath soaps. Synthetic detergents which are sufficiently inexpensive and have the requisite lathering and cleaning power make bars which are generally unsatisfactory due to high hygroscopicity, unsatisfactory solubility characteristics, extreme defatting action on the skin, poor working properties in standard soap machinery, brittleness and poor cohesion or excessive softness of the bar itself. For example, synthetic anionic surface active agents such as alkyl benzene sulfonates tend to produce a soft, sticky end product which is difficult to process and stamp into bars and the use of such materials in the production of solid detergent compositions is not desirable. More importantly, products produced therefrom are very irritating to the skin. In addition, conventional synthetic detergent bars generally tend to develop a very soft, sticky surface upon standing in contact with a wet surface and in many cases they do not possess adequate physical strength, readily cracking and crumbling during use.
There have been numerous attempts to replace soap with synthetic detergent toilet bars that overcome these shortcomings as well as to achieve a toilet bar which is mild and non-injurious to the skin while possessing good detergency and lathering quality when used on the skin and other surfaces in all types of water. A variety of synthetic detergents such as alkyl sulfates, alkane sulfonates, olefin sulfonates, mono-alkyl sulfosuccinates, coco methyl tauride and the like have been suggested for use in toilet bar compositions. These materials, although offering many advantages, are either too harsh in the ranges that they lather, require critical process conditions and special manufacturing equipment and, when toilet bars are prepared, the resulting product suffers severely in lathering characteristics and may be quite mushy.
Blending synthetic detergents with a binder system in an effort to formulate a mass with physical properties more like soap to overcome the problems of forming synthetic detergents into bars has also been attempted with some success. Ingredients generally constituting binder systems are wax-like, water insoluble fatty acids, fatty alcohols, mono-, di-, or triglycerides, fatty acid esters, particularly fatty acid esters with fatty alcohols, lanolin, petrolatum, etc.
More recently, the introduction of mild synthetic detergent toilet bars, especially those based on acyl isethionates such as sodium cocoyl isethionate as a primary ingredient, have met with growing commercial success. Such developments have been described, for example, in U.S. Pat. Nos. 3,901,832; 3,989,647; 4,007,125; 4,100,097; 4,110,239; 4,180,470; 4,211,675; 4,2311,904; 4,234,464, 4,268,424, 4,335,025, 4,959,171, 5,030,376, and EPO patent application 441,652. However, it is noted therein that such detergent bar formulations contain critical amounts and proportions of components and it is known that the toilet bars prepared therefrom generally exhibit disadvantages as to certain properties and manufacturing procedures. Accordingly, it is apparent that there is still a need for a toilet bar (syndet bar) made of conventional soap bar manufacturing equipment; lathers, foams, and wears well; exhibits minimal slushing and curd-forming properties in all types of water; possesses good plasticity and tactile characteristics and is mild and non-injurious to the user's skin.